Control systems which adjust the idle position of a butterfly valve using electro-mechanical drive assemblies may rely on an actual value sensor to measure the partial tilting of a butterfly valve in relation to the total possible tilting of the valve. Stated differently, an actual value sensor may be used to measure the degree to which a butterfly valve is actually open.
In such control systems, when the actual value sensor is used to measure the degree to which the butterfly valve is open only during idle operations, the relatively small range of movement which must be measured by the actual value sensor allows for accurate measurement at a high resolution. If, however, the actual value sensor is also used to measure the degree to which the butterfly valve is open during the full range of the motor's operations, as when it forms part of a speed control system, a much larger range of movement must be accurately measured. Because of this increased range of movement, the resolution of measurements by the actual value sensor decreases. This requires electronics matched to the evaluation of the butterfly valve position, a relatively expensive process. The invention described below reduces such costs by eliminating the need for adjustments to the electronic system through use of an actual value sensor which retains high resolution during idle adjustments.